1. Field of the invention:
This invention relates to a method for the production of semiconductor devices made of III-V group compounds. More particularly, it relates to a method for the production of semiconductor devices in which the heat-temperature of a substrate is reduced, resulting in high-quality crystalline layers; source gases are selectively decomposed thereby attaining composition control at the interface between the crystalline layers and composition control within the surface of each of the crystalline layers, and amount control of dopants; or the etching of the substrate is selectively achieved.
2. Description of the prior art:
A method for the production of semiconductors made of III-V group compounds, in which organic metal compounds are used, is disclosed in Japanese Patent Publication No. 49-44788. This method is disadvantageous in that, in the thermal decomposition of the organic metals and hydrides of V group compounds, when a compound semiconductor especially containing Pp such as InP, etc., is formed, a source gas such as PH.sub.3 is not decomposed, but it reacts with the organic metals to form polymer intermediates such as (-InMePH-)n, and moreover, in that when the crystalline layer formation step is carried out at high temperatures, P is removed from the compound semiconductor.
In order to eliminate the above-mentioned problems, a method in which a substrate is irradiated with laser light has been proposed in, for example, Japanese Laid-Open Patent Application No. 59-87814, wherein the substrate is irradiated with laser light having energy that is equal to or higher than the decomposition energy of the organic metals and/or PH.sub.3 so as to accelerate the decomposition of the source gases, and moreover, the substrate is irradiated with infrared laser light such as that from a carbon dioxide laser so as to reduce the growth temperature of the crystalline layers. However, it is extremely difficult to use such a method for the following reasons: The decomposition energy of the source gases is so high, 5-6 eV, that laser light sources having a wavelength of 200 nm or less must be used. Moreover, the most effective decomposition of the source gases can be achieved when the substrate is irradiated with laser light having energy equal to the composition energy of the source gases, but in order to achieve such decomposition, laser light sources capable of changing the wavelength of light in a wide range must be used, which is difficult to carry out. Moreover, the reduction of the growth temperature with the use of the irradiation with a carbon dioxide gas laser results in a rise of the surface temperature of the substrate, which diminishes the reduction of the said growth temperature.
Thus, the conventional use of irradiation with laser light has not yet resolved the above-mentioned problems.
On the other hand, the irradiation of a substrate with laser light is carried out so as to achieve the selective growth of semiconductor layers on the substrate based on the selective decomposition of source gases within the surface of the substrate and so as to achieve the selective etching of the substrate by the introduction of etching gases into the substrate. However, these processes require large equipment for the deflection of laser light, which causes difficulties in a practical use. For the said selective growth and the said selective etching, the use of elelctron beams instead of laser light has been proposed by, for example, S. Matsui et a., Jour. Vac. Sci & Technol. B vol. 4, Jan.-Feb., (1986). The apparatus used therefor is shown in FIG. 3, wherein a semiconductor substrate 3 disposed within a reaction tube 2 is directly irradiated with electron beams 5 from an electron gun 1, and source gases are introduced into the reaction tube 2 through the gas inlet 4. However, in order to directly irradiate the substrate 3 with the electron beams 5, the electron beams 5 must be accelerated at a level of several tens of electronvolts or more, so that energy of the electron beams must be several tens of electronvolts or more that is much higher than the decomposition energy of the source gases, which makes the selective decomposition of the source gases difficult, causing difficulties in composition control of grown layers. In addition, the direct irradiation of the substrate with the electron beams having high energy as mentioned above gives a high impact to the crystalline layers to be grown on the substrate, so it is sometimes difficult to obtain high-quality crystalline layers. As mentioned above, the direct irradiation of semiconductor substrates with high-energy electron beams involves many disadvantages and deficiencies.